Asymmetric hydrogenation sulfoxides

On the other hand, James reported, in 1976, the use of a chiral sulfoxide as a ligand of ruthenium for the asymmetric hydrogenation of itaconic acid, providing a low enantioselectivity of 12% ee (Scheme 8.23). ... 

In contrast, synthesis of 3,4-diphosphorylthiophenes requires more elaboration because of low reactivity of 3,4-positions of thiophene and unavailability of 3,4-dihalo or dimetallated thiophenes. Minami et al. synthesized 3,4-diphosphoryl thiophenes 16 as shown in Scheme 24 [46], Bis(phosphoryl)butadiene 17 was synthesized from 2-butyne-l,4-diol. Double addition of sodium sulfide to 17 gave tetrahydrothiophene 18. Oxidation of 18 to the corresponding sulfoxide 19 followed by dehydration gave dihydrothiophene 20. Final oxidation of 20 afforded 3,4-diphosphorylthiophene 16. 3,4-Diphosphorylthiophene derivative 21 was also synthesized by Pd catalyzed phosphorylation of 2,5-disubstituted-3,4-dihalothiophene and converted to diphosphine ligand for Rh catalysts for asymmetric hydrogenation (Scheme 25) [47],... 

Similar studies have been performed on rhodium(I) complexes of monodentate and potentially chelating sulfoxides (301, 307), again with rather mixed results. Complexes of the type [Rh(diene)(PPh3) (sulfoxide)]+ have been synthesized (302,306) for a range of chiral sulfoxides where coordination appears to be via oxygen, but attempts to asymmetrically hydrogenate itaconic acid using these precursors were... 

Ruthenium and Rhodium Hydrides Containing Chiral Phosphine or Chiral Sulfoxide Ligands, and Catalytic Asymmetric Hydrogenation... 

The TFE- or HFIP-activated H2O2 oxidant promotes not only epoxidation [34, 47, 48], but also Baeyer-Villiger oxidation [48], oxidation of sulfides to sulfoxide [34, 49], and oxidation of thiols to disulfides [5, 50]. The nature of the weaker nucleophilicity and higher acidity of TFE as compared with ethanol is useful as a solvent for Pd-catalyzed asymmetric hydrogenation of trifluoromethylimines [51]. 

Crystallization to obtain the major diastereomer in pure form is possible in some cases. These hydrogen-bonded vinylic sulfoxides undergo asymmetric 2 + 4-cycloaddition reactions with 1,3-cyclopentadiene (see p. 845). 

In addition, it has been observed that iridum complexes generated in situ from (TrCl3-3H20] and chiral sulfoxides cause no asymmetric induction during hydrogenation (300). 

Since the first report of the nonequivalence phenomenon, approximately 40 chiral substances have been reported to induce enantiomeric nonequivalence in the NMR spectra of a host of solutes. These CSAs are encountered in subsequent discussions. Two qualities considered to be essential in the design of the first reported experiment (3) are evident in nearly all CSA-solute combinations. In all cases, the CSA and the solute have the common feature of complementary functionality, which permits their interaction. Both are in general hydrogen bond donors or acceptors the CSAs are acids, amines, alcohols, sulfoxides, or cyclic compounds such as cyclodextiins, crown ethers, or peptides, which attractively interact with appropriate enantiomeric solutes, engendering different spatial environments for their nuclei. In nearly every case the CSA contains a group of high diamagnetic anisotropy near its asymmetric center, a feature... 

Reactions where NLE have been discovered include Sharpless asymmetric epoxi-dation of allylic alcohols, enantioselective oxidation of sulfides to sulfoxides, Diels-Alder and hetero-Diels-Alder reactions, carbonyl-ene reactions, addition of MesSiCN or organometallics on aldehydes, conjugated additions of organometal-lics on enones, enantioselective hydrogenations, copolymerization, and the Henry reaction. Because of the diversity of the reactions, it is more convenient to classify the examples according to the types of catalyst involved. 

This procedure was extended to a method for asymmetric synthesis of optically active epoxides starting from optically active sulfoxides. As the oxiranyUithium 131 reacts with the acidic hydrogen of the n-butyl aryl sulfoxide, the introduction of electrophiles to the reaction mixture was problematic. Therefore, the reaction was performed by addition of 1 equivalent of f-C4H9Li at — 100°C to 130 and the sulfoxide-lithium exchange reaction was found to be extremely rapid (within a few seconds at this temperature). Moreover, as f-butyl aryl sulfoxide 138 has now no more acidic hydrogen, the addition of several electrophiles leads to functionalized epoxides 139 (equation 48). ... 

Asymmetric sulfoxidation of aryl methyl sulhdes wra hydrogen... 

ASYMMETRIC SULFOXIDATION OF ARYL METHYL SULFIDES WITH HYDROGEN PEROXIDE IN WATER... 

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